When optical waves of different wavelengths propagate along an optical fiber, they do so at different group velocities. This so-called chromatic, or group-velocity dispersion causes pulse broadening which limits the rate at which information can be carried through an optical fiber. Recently, there has been interest in dispersion compensators that use dual-mode fibers operated in the LP.sub.11 spatial mode, close to their cutoff wavelength. Because higher-order spatial modes in optical fibers exhibit large, negative chromatic dispersion, such an arrangement provides a means for compensating for the positive dispersion in conventional single-mode fiber spans. See, for example, U.S. Pat. No. 5,185,827, issued Feb. 9, 1993, and assigned to applicant's assignee.
The attractiveness of using a dual-mode fiber for dispersion compensation stems from the ability to achieve large negative waveguide dispersion by operating close to the cutoff wavelength of the LP.sub.11 mode, thereby minimizing the amount of fiber required to compensate a given amount of positive dispersion. However, operation close to cutoff greatly increases sensitivity to bending losses, and it is these losses that place a practical limit on how much dispersion compensation can be realized.
It is, accordingly, the object of the present invention to minimize bending losses in dual-mode fiber dispersion compensators.